Project Summary: Polycystic ovarian syndrome (PCOS) is the leading cause of infertility worldwide. The cardinal features of the syndrome are anovulatory and cystic ovaries, disrupted menstrual cycles and hyperandrogenism. The ovaries are controlled by a small group of neurons that reside in the hypothalamus, gonadotropin-releasing hormone (GnRH) neurons. Activity in these neurons regulate pulsatile luteinizing hormone (LH) release from the pituitary gland, which controls ovulation and sex steroid hormone production at the ovary. Steroid hormones, in turn, act in the brain through an afferent neuronal network to provide critical feedback to GnRH neurons. In many women with PCOS this feedback pathway is impaired, resulting in increased GnRH/LH pulse frequency which drives the downstream consequences of the syndrome. Neurons upstream from GnRH neurons that co-express the peptides Kisspeptin, Neurokinin B and Dynorphin (KNDy neurons) are heavily implicated in both steroid hormone feedback and GnRH/LH pulse generation, therefore, perturbations in the normal function of this population may manifest as the PCOS neuroendocrine phenotype. However, recent evidence indicates that steroid hormone signaling does not occur directly at the level of KNDy neurons, implicating impaired steroid hormone feedback occurs within a population upstream to KNDy neurons. As the identity of afferents to KNDy neurons is largely unknown, the long term goal of this research is to characterize the phenotype and functional roles of neuronal populations that regulate KNDy neuron activity, and, determine whether changes in the identified neurons contribute to the pathophysiology of PCOS. To achieve this, we will use a well characterized mouse model of PCOS induced by prenatal androgen treatment. The mentored phase of this proposal will include a sophisticated combination of transgenic mice, rabies-mediated tract tracing techniques, whole brain optical clearing and three-dimensional analysis to define the upstream KNDy neuronal populations and determine whether impaired GnRH/LH hypersecretion is the result of altered synaptic input to KNDy neurons (Aim 1) and/or altered activity of afferents to KNDy neurons (Aim 2). At the end of my mentored phase, I will have gained expertise in neuroanatomical techniques necessary for transitioning to independence in my field and trained in functional techniques required for the Independent phase of this proposal. In Aim 3, I will use chemogenetic and/or optogenetic tools to define whether changes in the regulation of KNDy neurons by afferent populations is sufficient to increase GnRH/LH pulsatile release. In Aim 4, I will use viral-mediated deletion techniques to confirm that impaired steroid hormone sensitivity in afferent neurons drives downstream changes and results in the PCOS phenotype of impaired steroid hormone feedback and resultant infertility. These studies have the potential to identify new components of the circuitry critical for the neuronal control of fertility, and may provide novel targets for the therapeutic treatment of PCOS in adulthood, or, to prevent the development of the disorder in young women.